Blossoming Love

I have really liked this girl for the past couple weeks and things have been going great. I don't have many classes with her, but we do talk quite often. But I have two problems. First, I need to get her number soon. I am nervous since I haven't asked for a number in a long time, and I want to get some advice on what to say. My other problem is that we have a school trip to the movies. We haven't talked much about it but I would love to sit next to her during the movies. I don't know whether or not it is too soon to ask to sit next to her. The movie trip is in 3 days so your help would be quite appreciated! Thanks!